Variable inductor



1966 w. HOTINE ETAL 3,267,401

VARIABLE INDUCTOR Filed Oct. 22, 1965 Maui.

17 FEEE/T /j3 7 12 I I U 1 I 11 D/ELECTeIC J0 FEEe/TE 445M852 U it St te P t v 3,26 ,,401 VARIABLE INDUCTOR William Hotine, Idyllwild, and Stephen W. Babcock,

Pomona, Calif., assignors to General Dynamics Corporation, a corporation of Delaware Filed Oct. 22, 1965, Se!- No. 501,471 9 Claims. (Cl. 336-136) This invention relates generally to high frequency signaling systems and more particularly to a method of tuning high frequency signaling and to the construction of a variable high frequency inductor.

It has been a problem in V.H.F. circuitry to provide a stable miniature adjustable inductor having a high Q for use as a tank circuit element. Previous to this time, fixed inductors have been used in conjunction withvariable capacitors, due to the lack of a suitable variable inductor for V.H.F. tank circuits.

The present invention provides such a miniature, high Q variable inductor unit by a novel arrangement wherein the helical coil of the unit performs the double duty of serving as a tuning and locking thread member and as an inductive coil member. By this arrangement a considerable space saving is made possible with maximum coil Q and mechanical stability.

Therefore, it is an object of this invention to provide a variable inductor.

A further object of the invention is to provide a miniature adjustable inductor having a high Q.

Another object of the invention is to provide a miniature, high Q, variable inductor unit wherein the helical coil thereof serves as a tuning and locking member and as an inductive coil member.

Another object of the invention is to provide a variable inductor for V.H.F. tank circuits having maximum coil Q and mechanical stability while providing considerable space savings.

Other objects of the invention will become readily apparent from the following description and accompanying drawings wherein:

FIG. 1 is a sectional view of an embodiment of the invention; and

FIG. 2 is an end view of the FIG. 1 inductor.

Broadly, the invention relates to a variable inductor comprising a shielding cylinder coated on its internal surface with a suitable dielectric, a helicoil having cylinder thread matching turns and a radially deformed locking turn, and a tuning slug threaded so as to be screwed int-o the coil turns. In construction, the helicoil is screwed into the internal threaded dielectric surface of the cylinder and the tuning slug is then screwed into the coil to a depth where the presence of the slug deforms the coils locking turn so as to provide a position maintaining friction lock. 7

Referring now to the drawings, a cylindrical ferrite external core member 10 is coated on the internal surface with a dielectric plastic or ceramic layer 11 of a suitable depth, and an internal V thread 12 is formed in layer 11 by a suitable method such as tapping or molding. The size of thread 12 is the proper size for accepting therein a helicoil insert 13 which, for example, may be constructed of beryllium copper plated with silver. The helicoil insert 13 is of an internal locking type which has a hexagonal radially deformed lock-ing turn 14, and is inserted into the ferrite cylinder 10 by screwing the helicoil into the internal threads 12 in plastic layer 11. Terminal lugs 15 are welded to the ends of coil 13, and project outwardly to afford external connections to the inductor unit. An externally threaded ferrite tun-ing slug 16 having threads 17 which cooperate with the internal surface of the coils of helicoil insert 13, may be screwed into the coil axially to provide inductance variation of the unit. Locking turn 14 must be distended due to its shape when the threads 17 of slug 16 enter it, and this results in a friction lock of slug 16, which will maintain its adjusted position regardless of shock and vibration.

The dielectric layer 11 should preferably be of a low loss, mechanically stable, material with a low temperature coefiicient of expansion, such as a glass filled polycarbonate plastic.

The ferrite material of core member 10 and slug 16 should be of maximum suitability for the frequencies of interest and have high permeability and low losses.

While not shown, cylindrical core 10 may be provided with a few longitudinal slots, and taps can be attached to helicoil 13 at various points, for circuitry requiring them. Also, core 10 may be made of an insulating material-instead of ferrite, whereby a higher ratio of inductance variation may be obtained with less total inductance, but with no shielding as provided in the illustrated embodiment.

In addition, helicoil 13 may be made of any cross-sectional configuration and any pitch, if slug 16 is suitably threaded to match therewith and be retained therein by the locking turn of the coil.

It is thus seen that the present invention provides a unique variable inductor which greatly advances the art, particularly in V.H.F. circuitry and which has a high Q and is capable of being miniaturized.

Although a particular embodiment of the invention has been illustrated and described, modifications will become apparent to those skilled in the art, and it is intended to cover in the appended claims all such modifications as come Within the true spirit and scope of the invention.

What we claim is:

1. A variable inductor comprising: a magnetic shielding cylinder coated on the internal surface thereof with a suitable dielectric, said dielectric coating being provided with threads on the internal surface thereof, a helicoil having turns matching said threads and a radially deformed locking turn, said helicoil being operatively positioned at least partially within said cylinder, and a tuning slug having threads thereon which cooperate with the turns of said helicoil, whereby said tuning slug is adjustably screwed into said helicoil and the threads thereon cooperate with said locking turn so as to provide a position maintaining friction lock therebetween.

' 2. The variable inductor defined in claim 1, wherein said cylinder and said tuning slug are constructed of a ferrite material.

3. The variable inductor defined in claim 1, wherein said helicoil is constructed of beryllium copper plated with silver.

4. The variable inductor defined in claim 1, wherein said dielectric coating is composed of a low loss, mechanically stable material having a low temperature coefficient of expansion.

5. The variable inductor defined in claim 4, wherein said mechanically stable material is composed of a glass filled polycarbonate plastic.

6. A miniature variable inductor comprising: a cylindrical ferrite external core member coated on the internal surface to a suitable depth with a dielectric material, said dielectric material being provided with V-shaped threads across the length thereof, a helicoil insert of the internal locking type having a hexagonal radially deformed locking turn, the turns of said helicoil being configured to cooperate with said threads of said dielectric material whereby said helicoil is inserted into said cylinder, terminal members operatively connected to said helicoil, and an externally threaded ferrite tuning slug adjustably positioned in said helicoil by the cooperation of the threads thereon and the turns of said helicoil, said deformed locking turn being distended by said tuning slug and thereby providing a position maintaining friction lock therebetween.

7. The miniature variable inductor defined in claim 6, wherein said helicoil insert is constructed of beryllium copper plated with silver.

8. The miniature variable inductor defined in claim 6, wherein said tuning slug is constructed of ferrite material.

9. The miniature variable inductor defined in claim 6, wherein said dielectric material is of a low loss, mechanically stable type having a low temperature coefficient of expansion.

No references cited.

LEWIS H. MYERS, Primary Examiner. 

1. A VARIABLE INDUCTOR COMPRISING: A MAGNETIC SHIELDING CYLINDER COATED ON THE INTERNAL SURFACE THEREOF WITH A SUITABLE DIELECTRIC, SAID DIELECTRIC COATING BEING PROVIDED WITH THREADS ON THE INTERNAL SURFACE THEREOF, A HELICOIL HAVING TURNS MATCHING SAID THREADS AND A RADIALLY DEFORMED LOCKING TURN, SAID HELICOIL BEING OPERATIVELY POSITIONED AT LEAST PARTIALLY WITHIN SAID CYLINDER, AND A TUNING SLUG HAVING THREADS THEREON WHICH COOPERATE WITH THE TURNS OF SAID HELICOIL, WHEREBY SAID TUNING SLUG IS ADJUSTABLY 